Papers by Vladimir Bashkirov
2015 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2015
Particle tracking technology is currently being explored with Monte Carlo simulation studies as w... more Particle tracking technology is currently being explored with Monte Carlo simulation studies as well as first experimental prototypes as a method to improve the planning and delivery accuracy of hadron therapy. Advanced particle tracking technology is required to provide large-area detectors capable of single-particle registration at high data rates for applications such as particle imaging and pencil beam monitoring. One such candidate large-area particle tracking detector is based on plasma panel sensors (PPS). The PPS is an inherently digital, high gain, novel variant of micropattern gas detectors inspired by many operational and fabrication principles common to plasma display panels (i.e. plasma-TV's). The initial results of a simulation study of a realistic PPS telescope design shows that this technology is comparable to, or better than, existing silicon sensors in terms of both particle energy loss through the detector and spatial resolution for particle imaging. Further i...
Physics in Medicine & Biology, 2018
Single-event ion imaging enables the direct reconstruction of the relative stopping power (RSP) i... more Single-event ion imaging enables the direct reconstruction of the relative stopping power (RSP) information required for ion-beam therapy. Helium ions were recently hypothesized to be the optimal species for such technique. The purpose of this work is to investigate the effect of secondary fragments on the image quality of helium CT (HeCT) and to assess the performance of a prototype proton CT (pCT) scanner when operated with helium beams in Monte Carlo simulations and experiment. Experiments were conducted installing the U.S. pCT consortium prototype scanner at the Heidelberg Ion-Beam Therapy Center (HIT). Simulations were performed with the scanner using the TOPAS toolkit. HeCT images were reconstructed for a cylindrical water phantom, the CTP404 (sensitometry), and the CTP528 (line-pair) Catphan R modules. To identify and remove individual events caused by fragmentation, the multistage energy detector of the scanner was adapted to function as a ∆E − E telescope. The use of the developed filter eliminated the otherwise arising ring artifacts in the HeCT reconstructed images. For the HeCT reconstructed images of a water phantom, the maximum RSP error was improved by almost a factor 8 with †These authors contributed equally to this work.
Proton computed tomography has been suggested as a means for maximizing the potential benefits of... more Proton computed tomography has been suggested as a means for maximizing the potential benefits of proton radiation therapy. By measuring individual proton energy losses after traversing an object and predicting paths of maximum likelihood through the image space, relative stopping power maps can be generated for treatment planning and image guidance. However, the processes of proton interaction with the imaged object lead to a number of challenges in the image reconstruction procedure. In this work we describe our approach to obtaining accurate relative stopping power maps in the shortest amount of time.
Reconstructed images based on GEANT4-simulated 200 MeV pCT data of the illustrated phantom.
Physics Letters B, 1997
A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significa... more A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significantly enhanced the acceptance for very low x and low Q 2 inelastic neutral current scattering, e + p → e + X, at HERA. A measurement of the proton structure function F 2 and the total virtual photon-proton (γ * p) cross-section is
Zeitschrift Fur Physik C-Particles and Fields, 1997
Physics Letters B, 1998
We have searched for the production of a selectron and a squark in e + p collisions at a center-o... more We have searched for the production of a selectron and a squark in e + p collisions at a center-of-mass energy of 300 GeV using the ZEUS detector at HERA. The selectron and squark are sought in the direct decay into the lightest neutralino in the framework of supersymmetric extensions to the Standard Model which conserve R-parity. No evidence for the production of supersymmetric particles has been found in a data sample corresponding to 46.6 pb −1 of integrated luminosity. We express upper limits on the product of the cross section times the decay branching ratios as excluded regions in the parameter space of the Minimal Supersymmetric Standard Model.
Physics Letters B, 2000
A search for the leptonic decays of W bosons produced in the reaction e + p → e + W ± X at a cent... more A search for the leptonic decays of W bosons produced in the reaction e + p → e + W ± X at a centre-of-mass energy of 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb −1. Three events consistent with W → eν decay are found, giving a cross section estimate of 0.9 +1.0 −0.7 ± 0.2 pb, in good agreement with the Standard Model prediction. The corresponding 95% C.L. upper limit on the cross section is 3.3 pb. A search for the decay W → µν has a smaller selection efficiency and yields no candidate events. Limits on the cross section for W production with large hadronic transverse momentum have been obtained. A search for high-transverse-momentum isolated tracks in events with large missing transverse momentum yields results in good agreement with Standard Model expectations, in contrast to a recent report by the H1 collaboration of the observation of an excess of such events.
Zeitschrift Fur Medizinische Physik, 2008
Evaluation and monitoring of the cancer risk from space radiation exposure is a crucial requireme... more Evaluation and monitoring of the cancer risk from space radiation exposure is a crucial requirement for the success of long-term space missions. One important task in the risk calculation is to properly weigh the various components of space radiation dose according to their assumed contribution to the cancer risk relative to the risk associated with radiation of low ionization density. Currently, quality factors of radiation both on the ground and in space are defined by national and international commissions based on existing radiobiological data and presumed knowledge of the ionization density distribution of the radiation field at a given point of interest. This approach makes the determination of the average quality factor of a given radiation field a rather complex task. In this contribution, we investigate the possibility to define quality factors of space radiation exposure based on nanodosimetric data. The underlying formalism of the determination of quality factors on the basis of nanodosimetric data is described, and quality factors for protons and ions (helium and carbon) of different energies based on simulated nanodosimetric data are presented. The value and limitations of this approach are discussed.
IEEE Nuclear Science Symposium Conference Record, 2007
We report the results of a beam experiment to develop proton Computed Tomography (pCT). The setup... more We report the results of a beam experiment to develop proton Computed Tomography (pCT). The setup consists of telescopes of silicon strip detectors at the entrance and exit of a phantom to predict the path of the proton within the phantom and of a crystal calorimeter to measure the proton energy loss with high precision. The energy loss permits calculating the integrated proton stopping power along each proton path from which the electron density distribution can be reconstructed. We describe the 2D-image reconstruction of a lowcontrast phantom, derive the relationship between contrast, pixel size, and dose, and study the spatial resolution achievable with this setup .
Physics Letters B, 2000
The dependence of the photon structure on the photon virtuality, Q 2 , is studied by measuring th... more The dependence of the photon structure on the photon virtuality, Q 2 , is studied by measuring the reaction e + p → e + + jet+ jet+ X at photon-proton centre-of-mass energies 134 < W < 223 GeV. Events have been selected in the Q 2 ranges ≈ 0 GeV 2 , 0.1-0.55 GeV 2 , and 1.5-4.5 GeV 2 , having two jets with transverse energy E jet T > 5.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, x OBS γ. The ratio of the dijet cross section with x OBS γ < 0.75 to that with x OBS γ > 0.75 decreases as Q 2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can be interpreted in terms of a resolved photon component that falls with Q 2 but remains present at values of Q 2 up to 4.5 GeV 2. However, none of the models considered gives a good description of the data.
Physics Letters B, 2002
Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector a... more Searches in ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e + p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb −1. Excited electrons have been sought via the decays e * → eγ, e * → eZ and e * → νW. Excited quarks have been sought via the decays q * → qγ and q * → qW. A search for excited neutrinos decaying via ν * → νγ, ν * → νZ and ν * → eW is presented using e − p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb −1. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses 250 GeV.
Physics Letters B, 1995
The exclusive production of p" mesons in deep inelastic electron-proton scattering has been studi... more The exclusive production of p" mesons in deep inelastic electron-proton scattering has been studied using the ZEUS detector. Cross sections have been measured in the range 7 < Q2 < 25 GeV* for y*p centre of mass (c.m.) energies from 40 to 130 GeV. The y*p-f pup cross section exhibits a Q-~4~2*0~8~~~) dependence and both longitudinally and transversely polarised p"'s are observed. The y*p-+ p"p cross section rises strongly with increasing c.m. energy, when compared with NMC data at lower energy, which cannot be explained by production through soft pomeron exchange. The data are compared with perturbative QCD calculations where the rise in the cross section reflects the increase in the gluon density at low X.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2003
We report progress on a feasibility study of Proton Computed Tomography and Proton Transmission R... more We report progress on a feasibility study of Proton Computed Tomography and Proton Transmission Radiography for applications in treatment planning and patient positioning for proton radiation therapy. We analyzed data from proton transmission studies through a hollow aluminum cylinder taken with a telescope of silicon detectors with very high spatial and good energy resolution. In addition, we explored the usefulness of applying a cut on the angular divergence of the transmitted beam in a GEANT4 simulation study.
IEEE Transactions on Nuclear Science, 2006
IEEE Transactions on Nuclear Science, 2004
Proton computed tomography (pCT) has the potential to improve the accuracy of dose calculations f... more Proton computed tomography (pCT) has the potential to improve the accuracy of dose calculations for proton treatment planning, and will also be useful for pretreatment verification of patient positioning relative to the proton beam. A design study was performed to define the optimal approach to a pCT system based on specifications for applications in proton therapy. Conceptual and detailed design of a pCT system is presented; the system consists of a silicon-based particle tracking system and a crystal calorimeter to measure energy loss of individual protons. We discuss the formation of pCT images based on the reconstruction of volume electron density maps and the suitability of analytic and statistical algorithms for image reconstruction.
IEEE Transactions on Nuclear Science, 2007
As part of a program to investigate the feasibility of proton computed tomography, the most likel... more As part of a program to investigate the feasibility of proton computed tomography, the most likely path (MLP) of protons inside an absorber was measured in a beam experiment using a silicon strip detector setup with high position and angular resolution. The locations of 200 MeV protons were measured at three different absorber depth of PolyMethylMethAcrylate-PMMA (3.75, 6.25 and 12.5 cm) and binned in terms of the displacement and the exit angle measured behind the absorber. The observed position distributions were compared to theoretical predictions showing that the location of the protons can be predicted with an accuracy of better than 0.5 mm.
IEEE Transactions on Nuclear Science, 2007
Proton therapy is a precise forms of radiation therapy that makes use of high energy proton compa... more Proton therapy is a precise forms of radiation therapy that makes use of high energy proton compared to the conventional, more commonly used and less precise x-ray and electron beams. On the other hand, to fully exploit the proton therapy advantages, very accurate quality controls of the treatments are required. These are mainly related to the dose calculations and treatment planning. Actually dose calculations are routinely performed on the basis of X-Ray computed tomography while a big improvement could be obtained with the direct use of protons as the imaging system. In this work we report the results of Monte Carlo simulations for the study of an imaging system based on the use of high energy protons: the proton Computed Tomography (pCT). The main limitation of the pCT and the current adopted technical solutions, based on the use of the Most Likely Path (MLP) approximation are illustrated. Simulation results are compared with experimental data obtained with a first prototype of pCT system tested with 200 MeV proton beams available at the Loma Linda University Medical Center (LLUMC) (CA).
IEEE Transactions on Nuclear Science, 2006
As we move into the new millennium, it is important that we improve our understanding of radiatio... more As we move into the new millennium, it is important that we improve our understanding of radiation effects on humans and nanoelectronic systems. This understanding is essential in a number of areas including radiation therapy for cancer treatment and extended human presence in outer space. Nanodosimetry in low-pressure gases enables measurement of the energy deposition of ionizing radiation on a scale equivalent to the dimensions of the DNA molecule. This is extremely important for not only biological applications but also electronic applications, as the effect of radiation on nanoelectronics needs to be determined before they are installed and deployed in complex radiation fields. However, before nanodosimetry can be widely applied, further investigation is required to link the output of gas-based nanodosimeters to the actual effect of the radiation on a biological or electronic system. The purpose of this research is to conduct nanodosimetric measurements of proton radiation fields at the proton accelerator of Loma Linda University Medical Center (LLUMC) and to develop a Monte Carlo simulation system to validate and support further developments of experimental nanodosimetry. To achieve this, measured ion cluster size distributions are compared to the output from the Monte Carlo simulation system that simulates the characteristics of the LLUMC beam line and the performance of the nanodosimeter installed on one of LLUMC's proton research beam lines.
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Papers by Vladimir Bashkirov